A known impulse-type sinking hydrant comprises a movable support in the upper end of which there is mounted a valve for the control of the impulse action, and a cylindrical housing connected at its bottom end to a water-air reservoir. Inside the movable support and the housing there are disposed two pipes, entering one into the other telescopically, from which the inner pipe is connected rigidly to an upright member and the valve for the control of the impulse action, while the outer pipe is rigidly fastened in the housing, passes through its bottom and is connected to the supply pipe conduit.
Another known sinking hydrant comprises a cylindrical housing, inside which there is mounted a movable upright member with a central longitudinal hole. The upright member ends with a closed fitted piston. In the external surface of the piston there is machined a ring-shaped groove, connected by means of radial passageways to the central passageway of the upright member.
A drawback of the known impulse-type sinking hydrant lies in that the telescopic pipes, disposed inside the movable upright member and the housing, make difficult the sealing of the movable components of the hydrant, increase the hydraulical losses during irrigation and lead to an increase of the diametral sizes of the hydrant, which proportionally increase the resistance forces of the soil when the upright member is raised above the ground surface. Another drawback lies in the large, unproductive with respect to the irrigation, volume comprising the volume of the housing and the volume of the upright member, which leads to a several-times increase of the volume of the water-air reservoir.